The 'allure' of the Fronteris set is the bunker-like building (or rather its ceiling). It is the only box this can be acquired in. The rest is just the Ryza Ruins available separately or in Conquest (and of course the paper based content).
The best value of those three sets used to lie with the Munitorum set, followed by the Mechanicus and Fronteris sets. This was based on their price vs buying everything separately. As far as I know, the price has been raised though (from 65€ to 80€), so it might not be as good a deal anymore and the most 'important' aspect for these sets might come down to the exclusivity of some of the contents. The bunker in Fronteris and the pipes in Mechanicus are not available (anymore or never were) outside of those boxes. Everything in the Munitorum box is still available, so depends on the individual cost vs. the box to make a judgement.
Edited by gorg_graggel, 21 February 2021 - 11:13 PM.